Lung disease in cystic fibrosis (CF) is characterized by a profuse inflammatory response. Influx of large numbers of neutrophils results in secretions which contain a high concentration of extracellular leukocyte-derived DNA. Pulmozyme (dornase alfa) is a highly purified solution of recombinant human deoxyribonuclease (rhDNase), an enzyme with the specific function of cleaving extracellular DNA. Aerosolized Pulmozyme has been shown to be safe and effective in the treatment of CF lung disease. In a broad group of CF patients 5 years of age and older, Pulmozyme reduced the frequency of respiratory tract exacerbations requiring intravenous antibiotic therapy, and improved lung function as assessed by spirometry. The primary efficacy objective is to compare short-term improvement (14 days) in FEV1, produced by Pulmozyme (dornase alfa) administered via one of the two nebulizer systems. The secondary efficacy objective is to compare short-term improvement (14 days) in FVC and FEF25-75, produced by Pulmozyme (dornase alfa) administered via one of the two nebulizer systems. The safety objective is to compare the number and percent of adverse events in patients receiving Pulmozyme via one of the two nebulizer systems. Twelve patients have been enrolled at this site. No data analysis has been done.